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uk Home & property emergencies carbon monoxide alarm fault • co detector fault light • co alarm warning signal • carbon monoxide detector not working • co alarm chirping • co alarm beeping randomly • co alarm low battery • co alarm end of life • co detector error code • co alarm test button not working • carbon monoxide alarm silent • unsure if co alarm is real • co alarm false alarm worry • fuel burning appliance safety • boiler heater co concern • gas appliance carbon monoxide • co alarm reset confusion • tenant co alarm problem

What to do if…
your carbon monoxide detector shows a fault or warning signal and you’re not sure it’s working

Short answer

Treat it as potentially real until you’ve got everyone into fresh air. Once you’re outside, get the right help for the fuel source (gas emergency line if gas), and only then troubleshoot or replace the alarm.

Do not do these things

  • Do not ignore it, “sleep on it”, or assume it’s just a glitch if you’re unsure.
  • Do not keep using anything that burns fuel (boiler, gas cooker, fire, log burner, portable heater) “until you’re sure”.
  • Do not stay inside to “air it out”. If you can, open doors/windows as you leave.
  • Do not silence/reset and then carry on in the property.
  • Do not re-enter to “just grab something” if anyone feels unwell, if the alarm sounded like an actual CO alarm, or if you’ve been told to stay out.

What to do now

  1. Get everyone (and pets) into fresh air first. Go outdoors or to a place you can breathe clean air.
  2. Check for symptoms quickly. Headache, dizziness, nausea, confusion, unusual tiredness, or multiple people feeling unwell in the same place are red flags.
    • If severe symptoms or someone collapses: call 999.
    • If you feel unwell or worried after possible exposure: call NHS 111 for urgent advice.
  3. If gas could be involved (or you’re not sure), call the gas emergency number from outside:
    • Great Britain (England, Scotland, Wales): 0800 111 999 (National Gas Emergency Service, 24/7).
    • Northern Ireland: 0800 002 001 (NI Gas Emergency Service, 24/7). Follow their instructions.
  4. Stop using all fuel-burning appliances. Do not relight or restart anything until it’s been checked if there’s any chance this was a real CO warning.
  5. Only once you’re safe, work out whether this was a device fault vs a CO alarm:
    • Look at the label on the alarm for the model and check the display/LED pattern (faults are often “low battery” or “end-of-life”).
    • If it has replaceable batteries, replace them (don’t mix old/new).
    • If it indicates end-of-life or you can’t clear a fault after battery change/test, replace the whole alarm promptly.
  6. Arrange a qualified check before resuming normal use if there’s any doubt.
    • For gas appliances, use a Gas Safe registered engineer, especially if the alarm sounded like a real alarm, anyone had symptoms, or the emergency line advised it.
    • If you rent, tell your landlord/agent immediately and ask for a safety check and alarm replacement if needed.
  7. Re-enter only if it’s clearly a device fault (e.g., low battery/end-of-life), nobody is unwell, and there was no “CO alarm” sound/message. Keep it brief, don’t restart any fuel-burning appliance, and leave again if anything feels “off”.

What can wait

  • You do not need to figure out the exact cause or “prove” there was carbon monoxide right now.
  • You do not need to decide today whether to report anything or argue about responsibility (landlord vs. tenant vs. appliance).
  • You do not need to deep-research alarm standards or do DIY repairs on boilers/heaters.

Important reassurance

It’s common to feel unsure because different alarms use different beep/flash patterns for low battery, fault, end-of-life, and CO detected. If you can’t confidently tell which it is, treating it seriously first is the safest move.

Scope note

These are first steps to keep you safe and prevent a bad call in the moment. A qualified professional may be needed to confirm the source and make the property safe before you return to normal use.

Important note

This is general information, not a professional safety inspection or medical advice. If anyone is unwell, if your alarm sounded like a real CO alarm, or if you suspect a fuel-burning appliance is involved, get urgent help and professional checks.

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